The present invention relates to an improved cast iron material, and particularly to an improved cast iron brake drum having a compacted graphite micro structure disposed within a primarily pearlitic metallurgical structure.
Brake drums are widely employed in all vehicles having different types of cast iron brake drums. In service, these drums often times encounter strenuous work conditions, and thereby desirably employ materials that will exhibit excellent wear resistance, strength, and heat conductivity. In view of the complexities of the shape, and taking into account other material properties and processes requirements; it has been common to manufacture brake drums with a gray cast iron material.
The use of presently employed casting materials has presented limitations in improving the design of brake drums, especially in reducing part weight. By way of example, the trend has been towards reducing weight by casting gray iron against a steel shell to reduce the weight of the brake drums. These composite brake drums significantly increase production time and costs. Absent additional expensive, time consuming, and potentially inefficient heat treatments or finishing steps, significant volumes of high integrity brake drum castings are often not obtainable over short periods of time.
Accordingly, even though light weight castings are achieved, the manufacturer of high integrity iron brake drums require expensive and substantial time consuming post-casting finishing steps. A system is needed that permits the casting of an integrally shaped article, particularly a brake component, which has excellent machinability, wear resistance, and high strength characteristics, as well as heat transfer characteristics. Additionally, the brake components must also meet all required brake component properties which are required of brake components. The microstructure should include a generally uniform dispersion of compacted forms of graphite (vermicular) in a pearlitic iron matrix.
The present invention satisfies the above by providing an improved system for making a cast iron article, particularly a cast brake component. The gray cast iron brake component for use in a braking system has a final composition of: from about 3.0 to about 4.0 percent carbon; about 2.15 to about 2.60 percent silicon; about 0.40 to about 0.90 manganese; and the balance iron. The compacted graphite iron brake component has a frictionally engageable portion with a microstructure containing compacted graphite disposed in a primarily pearlitic matrix. Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, the drawings, and appended claims.